Add a Remote Device Without a BBMD

You may encounter a situation where you must add a device on a different network. You may have no control of the BBMD configuration or you may have no BBMDs available due to poor device support. In these situations, you may have to add a remote device without a BBMD. It’s a handy trick, but not an ideal long-term situation.

How is that possible?

The BACnet Broadcast Management Device is required to route broadcasts between BACnet networks separated by routers. BACnet uses broadcast messages for device and point discovery, which are public requests by nature. However, if you know what devices are out there you don’t need discovery! You can add a remote device without a BBMD so long as you know the MAC addresses of the device in question.

What do we need?

You’ll need the device’s BACnet MAC address and BACnet instance number. The BACnet MAC address isn’t the same as the usual MAC address we’re familiar with in IT. A quick way to find it is to discover the device while you’re connected to its BACnet network directly and your BACnet client should tell you directly. Tridium’s N4 platform has a column dedicated to this field. For BACnet/IP devices, the MAC address is a combination of the IP address in hexadecimal and the BACnet/IP port in use.

For example, for an IP address of 192.168.1.6 and a default BACnet/IP port of 47808 (“BAC0”), the MAC address is C0A816BAC0 (192 -> 0xC0, 168 -> 0xA8, 1 -> 0x1, 6 -> 0x6).

Just add the device with the appropriate instance number and MAC address. With any luck, you should be fully communicating. However, the implementation specifics will vary wildly depending on what software you’re using.

Potential Problems

Though this technique can work well for diagnostic purposes, some devices will continue to assume good broadcast communication. If that communication isn’t possible, they’ll assume something is wrong. It’s common practice to use a Who-Is broadcast to check the network status of all devices on the network. If you manually add a remote device without a BBMD handling broadcasts, it will not see or respond to these requests and appear to be offline. You’ll need to get a BBMD in place to ensure your network runs smoothly in that scenario.